Chapter 301. Servlet Component

See Servlet Tomcat Example.

When using the Servlet component in a Camel/Spring application it’s often required to load the Spring ApplicationContext after the Servlet component has started. This can be accomplished by using Spring’s ContextLoaderServlet instead of ContextLoaderListener. In that case you’ll need to start ContextLoaderServlet after CamelHttpTransportServlet like this:

<web-app>
  <servlet>
        <servlet-name>CamelServlet</servlet-name>
        <servlet-class>
            org.apache.camel.component.servlet.CamelHttpTransportServlet
        </servlet-class>
        <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet>
        <servlet-name>SpringApplicationContext</servlet-name>
        <servlet-class>
            org.springframework.web.context.ContextLoaderServlet
        </servlet-class>
        <load-on-startup>2</load-on-startup>
  </servlet>
<web-app>

From Camel 2.6.0, you can publish the CamelHttpTransportServlet as an OSGi service with Blueprint like this:

<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="
           http://www.osgi.org/xmlns/blueprint/v1.0.0 https://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">

    <bean id="camelServlet" class="org.apache.camel.component.servlet.CamelHttpTransportServlet" />

    <!--
        Enlist it in OSGi service registry.
        This will cause two things:
        1) As the pax web whiteboard extender is running the CamelServlet will
           be registered with the OSGi HTTP Service
        2) It will trigger the HttpRegistry in other bundles so the servlet is
           made known there too
    -->
    <service ref="camelServlet">
        <interfaces>
            <value>javax.servlet.Servlet</value>
            <value>org.apache.camel.http.common.CamelServlet</value>
        </interfaces>
        <service-properties>
            <entry key="alias" value="/camel/services" />
            <entry key="matchOnUriPrefix" value="true" />
            <entry key="servlet-name" value="CamelServlet" />
        </service-properties>
    </service>

</blueprint>

Then use this service in your Camel route like this:

<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
           xmlns:ext="http://aries.apache.org/blueprint/xmlns/blueprint-ext/v1.0.0"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="
           http://www.osgi.org/xmlns/blueprint/v1.0.0 https://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">

    <reference id="servletref" ext:proxy-method="classes" interface="org.apache.camel.http.common.CamelServlet">
        <reference-listener ref="httpRegistry" bind-method="register" unbind-method="unregister" />
    </reference>

    <bean id="httpRegistry" class="org.apache.camel.component.servlet.DefaultHttpRegistry" />

    <bean id="servlet" class="org.apache.camel.component.servlet.ServletComponent">
        <property name="httpRegistry" ref="httpRegistry" />
    </bean>

    <bean id="servletProcessor" class="org.apache.camel.example.servlet.ServletProcessor" />

    <camelContext xmlns="http://camel.apache.org/schema/blueprint">
        <route>
            <!-- Notice how we can use the servlet scheme which is that reference above -->
            <from uri="servlet://hello" />
            <process ref="servletProcessor" />
        </route>
    </camelContext>

</blueprint>

For versions prior to Camel 2.6 you can use an Activator to publish the CamelHttpTransportServlet on the OSGi platform:

import java.util.Dictionary;
import java.util.Hashtable;

import org.apache.camel.component.servlet.CamelHttpTransportServlet;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import org.osgi.service.http.HttpContext;
import org.osgi.service.http.HttpService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.osgi.context.BundleContextAware;

public final class ServletActivator implements BundleActivator, BundleContextAware {
    private static final Logger LOG = LoggerFactory.getLogger(ServletActivator.class);
    private static boolean registerService;

    /**
     * HttpService reference.
     */
    private ServiceReference<?> httpServiceRef;

    /**
     * Called when the OSGi framework starts our bundle
     */
    public void start(BundleContext bc) throws Exception {
        registerServlet(bc);
    }

    /**
     * Called when the OSGi framework stops our bundle
     */
    public void stop(BundleContext bc) throws Exception {
        if (httpServiceRef != null) {
            bc.ungetService(httpServiceRef);
            httpServiceRef = null;
        }
    }

    protected void registerServlet(BundleContext bundleContext) throws Exception {
        httpServiceRef = bundleContext.getServiceReference(HttpService.class.getName());

        if (httpServiceRef != null && !registerService) {
            LOG.info("Register the servlet service");
            final HttpService httpService = (HttpService)bundleContext.getService(httpServiceRef);
            if (httpService != null) {
                // create a default context to share between registrations
                final HttpContext httpContext = httpService.createDefaultHttpContext();
                // register the hello world servlet
                final Dictionary<String, String> initParams = new Hashtable<String, String>();
                initParams.put("matchOnUriPrefix", "false");
                initParams.put("servlet-name", "CamelServlet");
                httpService.registerServlet("/camel/services", // alias
                    new CamelHttpTransportServlet(), // register servlet
                    initParams, // init params
                    httpContext // http context
                );
                registerService = true;
            }
        }
    }

    public void setBundleContext(BundleContext bc) {
        try {
            registerServlet(bc);
        } catch (Exception e) {
            LOG.error("Cannot register the servlet, the reason is " + e);
        }
    }

}

From Camel 2.19.0 onwards, the camel-servlet-starter library binds automatically all the rest endpoints under the /camel/* context path. The following table summarizes the additional configuration properties available in the camel-servlet-starter library. The automatic mapping of the Camel servlet can also be disabled.

You would need to chose one of the following implementations of the abstract class org.apache.camel.component.servletlistener.CamelServletContextListener.

To use this you need to configure the org.apache.camel.component.servletlistener.CamelServletContextListener in the WEB-INF/web.xml file as shown below:

The org.apache.camel.component.servletlistener.CamelServletContextListener supports the following options which can be configured as context-param in the web.xml file.

See Servlet Tomcat No Spring Example.

Available as of Camel 2.14/2.13.3/2.12.5

The created CamelContext is stored on the ServletContext as an attribute with the key "CamelContext". You can get hold of the CamelContext if you can get hold of the ServletContext as shown below:

ServletContext sc = ...
CamelContext camel = (CamelContext) sc.getAttribute("CamelContext");

You need to configure which routes to use in the web.xml file. You can do this in a number of ways, though all the parameters must be prefixed with "routeBuilder".

  <context-param>
    <param-name>routeBuilder-MyRoute</param-name>
    <param-value>org.apache.camel.component.servletlistener.MyRoute</param-value>
  </context-param>

  <context-param>
    <param-name>routeBuilder-routes</param-name>
    <!-- we can define multiple values separated by comma -->
    <param-value>
      org.apache.camel.component.servletlistener.MyRoute,
      org.apache.camel.component.servletlistener.routes.BarRouteBuilder
    </param-value>
  </context-param>

  <context-param>
    <param-name>routeBuilder-MyRoute</param-name>
    <!-- define the routes using package scanning by prefixing with packagescan: -->
    <param-value>packagescan:org.apache.camel.component.servletlistener.routes</param-value>
  </context-param>

  <context-param>
    <param-name>routeBuilder-MyRoute</param-name>
    <param-value>classpath:routes/myRoutes.xml</param-value>
  </context-param>

<?xml version="1.0" encoding="UTF-8"?>
<!-- the xmlns="http://camel.apache.org/schema/spring" is needed -->
<routes xmlns="http://camel.apache.org/schema/spring">

  <route id="foo">
    <from uri="direct:foo"/>
    <to uri="mock:foo"/>
  </route>

  <route id="bar">
    <from uri="direct:bar"/>
    <to uri="mock:bar"/>
  </route>

</routes>

  <!-- setup property placeholder to load properties from classpath -->
  <!-- we do this by setting the param-name with propertyPlaceholder. as prefix and then any options such as location, cache etc -->
  <context-param>
    <param-name>propertyPlaceholder.location</param-name>
    <param-value>classpath:myproperties.properties</param-value>
  </context-param>
  <!-- for example to disable cache on properties component, you do -->
  <context-param>
    <param-name>propertyPlaceholder.cache</param-name>
    <param-value>false</param-value>
  </context-param>

  <!-- configure JMX by using names that is prefixed with jmx. -->
  <!-- in this example we disable JMX -->
  <context-param>
    <param-name>jmx.disabled</param-name>
    <param-value>true</param-value>
  </context-param>

  <context-param>
    <param-name>CamelContextLifecycle</param-name>
    <param-value>org.apache.camel.component.servletlistener.MyLifecycle</param-value>
  </context-param>

public class MyBeanRoute extends RouteBuilder {
    @Override
    public void configure() throws Exception {
        from("seda:foo").routeId("foo")
            .to("bean:myBean")
            .to("mock:foo");
    }
}